CONTENTS Introduction

How it Works

Advantages of tidal energy

Disadvantages of tidal energy

Wave facts

World Wave power resources

Wave power design

INTRODUCTION The generation of tidal power electricity has a long utilization history

around the coastal areas of Great Britain and France, dating back to the 17th century. We can find historic relics of ocean hydro power implements and electricity generation in the previously mentioned areas. The major device of tidal electricity generation was simply a waterwheel at that time. Then, the electricity generation system gradually evolved to tidal electricity power plants on the basis of industrialization. The first tidal power station in France became operational in 1967; however tidal power stations are still few and uncommon nowadays because of their high establishment cost. Until now, in Canada, China and Russia, some tidal electricity power generation projects continue, but they are rarely put into practice. In today’s modern society, we suffer from serious energy shortages, which urge us to utilize all the new energy sources to meet the increasing demand. Consequently, we can expect more technology developments and investments in tidal power plants with more efficient equipment, and under budget.

HOW IT WORKS First generation, barrage-style tidal power plants

Works by building Barrage to contain water after high tide, then water has to pass through a turbine to return to low tide

Sites in France (La Rance), Canada (Annapolis), and Russia

Future sites possibly on Severn River in England, San Francisco bay, Passamaquoddy

Advantages of Tidal energy No pollution

Renewable resource

More efficient than wind because of the density of water

Predictable source of energy vs. wind and solar

Second generation has very few disadvantages Does not affect wildlife

Does not affect silt deposits

Less costly – both in building and maintenance

Disadvantages of Tidal Energy Presently costly

Expensive to build and maintain

A 1085MW facility could cost as much as 1.2 billion dollars to construct and run

Connection to the grid

Technology is not fully developed

Barrage style only produces energy for about 10 hours out of the day

Barrage style has environmental affects Such as fish and plant migration

Silt deposits

Local tides change- affects still under study

Wave Facts Waves are caused by a number of forces, i.e. wind, gravitational pull

from the sun and moon, changes in atmospheric pressure, earthquakes etc. Waves created by wind are the most common waves. Unequal heating of the Earth’s surface generates wind, and wind blowing over water generates waves.

This energy transfer results in a concentration of the energy involved: the initial solar power level of about 1 kW/m2 is concentrated to an average wave power level of 70kW/m of crest length. This figure rises to an average of 170 kW/m of crest length during the winter, and to more than 1 MW/m during storms.

Wave energy performance measures are characterized by diffuse energy, enormous forces during storms, and variation over wide range in wave size, length, period, and direction.

Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid.

World Wave power resources

World Energy Council 2001 Survey stated the "potential exploitable wave energy" resources worldwide to be 2 TW. For European waters the resource was estimated to be able to cover more than 50% of the total power consumption.The wave market is estimated at $32 billion in the United Kingdom and $800 billion worldwide.The United States has exhibited weak effort compared to overseas projects in Norway, Denmark, Japan and the United Kingdom.As of 1995, 685 kilowatts (kW) of grid-connected wave generating capacity was operating worldwide. This capacity comes from eight demonstration plants ranging in size from 350 kW to 20 kW. Until recently the commercial use of wave power has been limited to small systems of tens to hundreds of watts aboard generate power

Wave Power

Wave Power Designs

Wave power Although many wave energy devices have been

invented, only a small proportion have been tested and evaluated. Only a few of these have been tested at sea, in ocean waves, rather than in artificial wave tanks. Large scale offshore devices and small scale shoreline devices have been ocean tested.

The total power of waves breaking on the world's coastlines is estimated at 2 to 3 million megawatts. In favorable locations, wave energy density can average 65 megawatts per mile of coastline.

Oscillating Water Columns (OWC)These devices generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine.Floats or Pitching DevicesThese devices generate electricity from the bobbing or pitching action of a floating object. The object can be mounted to a floating raft or to a device fixed on the ocean floor. Wave Surge or Focusing DevicesThese shoreline devices, also called "tapered channel" systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. These focusing surge devices are sizable barriers that channel large waves to increase wave height for redirection into elevated reservoirs.

Oscillating Water Columns The Nearshore OWC rests directly on the seabed and is

designed to operate in the near-shore environment in a nominal mean water depth of 15m.

Nearshore OWC units also act like artificial reefs, improving environments for fishing while calming the water for a harbor.

OWC designs typically require high maintenance, costly, taut moorings or foundations for operation while only using the extreme upper strata of an ocean site for energy conversion. While focusing devices are less susceptible to storm damage, massive structuring renders them most costly among wave power plant types.

Since 1965, Japan has installed hundreds of OWC-powered navigational buoys and is currently operating two small demonstration OWC power plants. China constructed a 3 kW OWC and India has a 150 kW OWC caisson breakwater device.

A 75 kW shore-based demonstration plant by Queens University, Belfast, using the OWC process described above has operated on the Scottish island of Islay for 10 years

Floating Devices

The Salter Duck, Clam, Archimedes wave swing, and other floating wave energy devices generate electricity through the harmonic motion of the floating part of the device. In these systems, the devices rise and fall according to the motion of the wave and electricity is generated through their motion.

The Salter Duck is able to produce energy very efficiently, however its development was stalled during the 1980s due to a miscalculation in the cost of energy production by a factor of 10 and it has only been in recent years when the technology was reassessed and the error identified.

Tapered Channel Wave Power

These shoreline systems consist of a tapered channel which feeds into a reservoir constructed on a cliff. The narrowing of the channel causes the waves to increase their amplitude (wave height) as they move towards the cliff face which eventually spills over the walls of the channel and into the reservoir which is positioned several meters above mean sea level. The kinetic energy of the moving wave is converted into potential energy as the water is stored in the reservoir. The water then passes through hydroelectric turbines on the way back to sea level thus generating electricity.

This vs. That Advantages The energy is free - no fuel needed, no waste produced. Most designs are inexpensive to operate and maintain. Waves can produce a great deal of energy. There are minimal environmental impacts.

Disadvantages Depends on the waves - sometimes you'll get loads of energy, sometimes nothing. Needs a suitable site, where waves are consistently strong. Must be able to withstand very rough weather. Disturbance or destruction of marine life Possible threat to navigation from collisions because the wave energy devices rise only

a few feet above the water. Degradation of scenic ocean front views from wave energy devices located near or on

the shore, and from onshore overhead electric transmission lines.

Conclusion: Waves harness a lot of the sun’s power, but they are better for surfing than generating electricity.